1. Field of the Invention
This invention relates to the field of circulation systems for water tanks and more particularly to the field of circulation systems for enclosed tanks such as used for municipalities, fire protection, and industrial purposes.
2. Discussion of the Background
Municipalities, fire districts, and industries commonly use enclosed water tanks. Such tanks typically hold about 300,000-500,000 gallons with some larger ones more on the order of 2 to 3 million gallons and are about 50-75 feet wide and 30 or more feet high. The water in these tanks is preferably kept mixed by an internal circulation system to maintain its freshness, particularly in municipal water tanks, and to avoid water quality problems such as bacteria growth and nitrite development.
A physical problem with many such tanks is that they normally have only a relatively small access opening (e.g., 18-24 inches wide) which is designed primarily just to permit an individual worker to pass through to inspect or repair the tank. Consequently, many circulation systems if they are going to be used in the tank must be passed through the access opening in nearly completely disassembled or at least partially disassembled condition. One or more workers must then enter the tank to assemble the system. This often requires special, elaborate, and costly training and following strict regulatory and other safety procedures. Special equipment must also often be used such as winches to lower the workers, tethered tools, safety lines, air monitors, inflatable rafts, and even diving gear as well as rescue personnel standing by. Additionally, it can require that the tank be taken off line or out of service and even drained. Alternate sources must often then be arranged to temporarily supply water to customers and for fire protection. Any unexpected or prolonged delays in bringing the tank back on line can thereafter be quite costly and in some cases present safety concerns to the community. The same problems are presented if the circulation system placed in the tank subsequently breaks down and workers must enter the tank to repair it.
With these and other concerns in mind, the present invention was developed. In it, a submersible circulation system is provided that can easily fit through the relatively small access opening of the tank in a completely assembled condition. Additionally, the circulation system is designed to be lowered to the tank floor to automatically assume the desired operating orientation without the need for any workers to enter the tank. The system can also be raised out of the tank through the access opening without the necessity of any workers having to enter the tank.